1. Field of the Invention
The invention relates to a method for recuperating energy in a hybrid vehicle, which hybrid vehicle comprises an internal combustion engine and an electrical machine, and has an on-board electrical system comprising an energy store that can be charged with electrical energy by the electrical machine during the recuperation operation. The invention further relates to an apparatus for controlling a recuperation operation in a hybrid vehicle.
2. Description of the Related Art
Owing to increasingly stricter exhaust gas legislation and demands by vehicle owners for reduced operating costs, increasingly higher demands are being made of motor vehicles with respect to fuel consumption and pollutant emissions by the motor vehicles, while at the same time a higher degree of driving comfort is intended to be realized. In order to achieve this objective, it is known from practice to equip motor vehicles with an automatic stop/start apparatus by which the internal combustion engine can be automatically turned off and started under predetermined conditions. Therefore, the internal combustion engine is automatically turned off, for example, when no driving force is required while stopped at a traffic light. As soon as driving force is required again, that is to say when the traffic light turns to “green” and the driver operates the accelerator pedal, the vehicle is restarted by the electric motor. Fuel consumption by the vehicle can be reduced in this way.
Furthermore, it is known from practice to equip motor vehicles with recuperation systems. Hybrid vehicles of this kind usually comprise, in addition to the internal combustion engine, an electrical machine operated either in a motor mode or a generator mode depending on the driving situation. In the motor mode, the electrical machine generates an additional drive torque that assists the internal combustion engine, for example in an acceleration phase. In the generator mode however, the kinetic energy released during the deceleration of the vehicle is converted into electrical energy (recuperation). The electrical energy obtained in this way is stored in at least one energy store, such as an ultracapacitor store, and can be used in other driving situations, for example for driving the vehicle or for supplying power to electrical loads. The efficiency of the vehicle can be considerably increased in this way.
A conventional approach in vehicles of this kind is to make an attempt during the recuperation operation to exert as high as possible a proportion of the desired total deceleration, which the driver prespecifies, for example, by operating the foot brake pedal, by the generator to recover a maximum amount of energy. In vehicles of this kind, a common operating strategy is to perform recuperation with the maximum generator power during the recuperation operation, until the at least one energy store for receiving recuperation energy in the vehicle is full. However, the quantity of electrical energy that can be generated by the generator is dependent on the state of charge or the capacity of the energy store. In the case of a fully charged energy store, very little electrical energy or no electrical energy at all can be fed into the on-board electrical system since the energy store could otherwise be overloaded or voltage-sensitive loads could be damaged. The power output by the generator is accordingly adjusted by a regulator. This means that the generator (including the inverter) and the energy store are operated with high power losses and the energy store usually has a high energy level even though there are service life-optimum energy windows depending on the type of energy store. Particularly in the case of ultracapacitor storage devices, the fully charged state reduces the durability of the service life of the energy store to a disproportionately excessive extent.